I heard of Lorilee Lippincott by reading her Simplicity Parenting blog, and I was happy to see that one of her books was in my library system. She mentions Simplicity Parenting and Dave Ramsey's work as well as a few other inspirations. We're interested in the Dave Ramsey ideas and got a couple of books we haven't read yet. They'll come along as we continue to simplify.
I didn't read every word of this book, but I picked the areas I really wanted to check in with (as regards living simply), and her book is a nice thought-provoker. For example, she looks at a person's closet first in terms of what they'd consider ideal (which could even mean adding things to it). The ideals are considered first around the home, and that's connected to another book I'm in the middle of called Breathing Room: Open Your Heart by Decluttering Your Home.
This one compares rooms with parts of your heart and gives practical advice on several layers. It's not just about the stuff in this book--it's much more about what we're dealing with that is manifested in that clutter. There are simple guides for looking at each room and what you'd like to experience in that room.